It can be broadly described as infectious or non-infectious in origin. Infectious causes of diarrheoa can include infections with protozoa, bacteria, and viruses. Non-infectious causes may include food intolerances, pancreatitis, irritable bowel disease, hormonal imbalances (Addison’s), cancer, congenital abnormalities, organ dysfunction, toxin ingestion and so on. The initial work up is usually based on history, duration, clinical presentation, blood tests, faecal test and diagnostic imaging such as abdominal ultrasound.

Some infectious causes of bacterial in our companion animals can also be transmitted to us. This is known as zoonosis. A common zoonotic protozoa that affects companion animals is giardia. Giardia is estimated to affect around 5-15 per cent of cats and dogs. There is a number of different species but the most common in companion animals is Giardia dupdenalis, which can also infect people.

The protozoa are found in water, food and soil contaminated with affected faeces. Young or immunocompromised animals are more likely to be affected. The most common clinical sign is diarrheoa. It may be waxing or waning or continuous. Some animals will be asymptomatic carriers. Typically animals begin to shed the protozoa within 5-16 days of infection.

Cysts can be identified by performing a faecal sample, however, as they are spread intermittently, a negative test does not rule out infection and ideally screening should be carried out at least three times over five days.

Treatment can be challenging but is based around antibiotics and immune support.